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1.
利用 12年的Lageos 1卫星激光测距资料 (1990 - 2 0 0 1)解算得到了地球定向参数 (EOP) ,将该序列的结果与同期的EOP(IERS)C0 4进行比较 ,其外符精度为 :极移XP— 0 .4 0mas,YP— 0 .4 2mas ,日长变化Dr— 0 .0 35ms。 相似文献
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Yulia A. Chernetenko 《Celestial Mechanics and Dynamical Astronomy》2001,80(3-4):185-194
International programs of observations of selected minor planets have lasted about 50 years and the last one comes to the end in 2000. The main aim of these observational programs consists in obtaining the orientation of the stellar reference frame with respect to the dynamical one using observations of the bright minor planets. The observations are also useful for the orbital improvements of the asteroids themselves. They are available from the author via e-mail at the address .During the above mentioned period more than 23 000 observations of minor planets, referred to different reference star catalogues, have been obtained. The reduction procedure of observations to the PPM star catalogue is described. The orientation parameters are given and discussed. 相似文献
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If a magma is a hybrid of two (or more) isotopically distinctend-members, at least one of which is partially crystalline,separation of melt and crystals after hybridization will leadto the development of isotopic heterogeneities in the magmaas long as some of the pre-existing crystalline material (antecrysts)retains any of its original isotopic composition. This holdstrue whether the hybridization event is magma mixing as traditionallyconstrued, bulk assimilation, or melt assimilation. Once a magma-scaleisotopic heterogeneity is formed by crystal–melt separation,it is essentially permanent, persisting regardless of subsequentcrystallization, mixing, or equilibration events. The magnitudeof the isotopic variability resulting from crystal–meltseparation can be as large as that resulting from differentialcontamination, multiple isotopically distinct sources, or insitu isotopic evolution. In one model, a redistribution of one-thirdof the antecryst cargo yielded a crystal-enriched sample with87Sr/86Sr of 0·7058, whereas the complementary crystal-poorsample has 87Sr/86Sr of 0·7068. In other models, crystal-richsamples are enriched in radiogenic Sr. Isotopic heterogeneitiescan be either continuous (controlled by the modal distributionof crystals and melt) or discontinuous (when there is completeseparation of crystals and liquid). The first case may be exemplifiedby some isotopically zoned large-volume rhyolites, formed bythe eruptive inversion of a modally zoned magma chamber. Inthe latter case, the isotopic composition of any (for example)interstitial liquid will be distinct from the isotopic compositionof the bulk crystal fraction. The separation of such an interstitialliquid may explain the presence of isotopically distinct late-stageaplites in plutons. Crystal–melt separation provides anadditional option for the interpretation of isotopically zonedor heterogeneous magmas. This option is particularly attractivefor systems whose chemical variation is otherwise explicableby fractionation-dominated processes. Non-isotopic chemicalheterogeneities can also develop in this fashion. KEY WORDS: isotopic heterogeneity; zoning; hybrid magma; crystal separation; Sr isotopes; aplite; rhyolite 相似文献
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